Dynamic control of DRM and RWGS reactions over Ru/YSZ catalysts by applied potential: insights into mechanisms and selectivity

Abstract

This study explores the electrochemical promotion of dry reforming of methane (DRM) and reverse water–gas shift (RWGS) reactions over a ruthenium (Ru) catalyst supported on yttria-stabilized zirconia (YSZ). Physicochemical properties were examined using a range of surface and structural characterization techniques. Ru remained metallic after reaction, with minor oxidation under high CO₂ concentrations. While carbon was detected under all conditions, only oxidizing environments led to the accumulation of oxidized species, indicating surface-bound intermediates. Catalytic behavior was investigated under reducing (P_CH4 = 4 kPa, P_CO2 = 1 kPa) and stoichiometric (P_CH4 = 1 kPa, P_CO2 = 1 kPa) conditions. DRM dominated under reducing conditions, while stoichiometric feeds led to competition between DRM and RWGS, showing inverted volcano behavior. Positive polarization (+1 V) enhanced CO production by improving CH₄ adsorption, while negative polarization (−1 V) suppressed DRM and favored RWGS. Electrochemical promotion of catalysis (EPOC) was quantified by measuring the rate enhancement ratios (ρ). Under reducing conditions, positive polarization increased DRM rates tenfold at low temperatures, with reduced effect at higher temperatures. In contrast, negative polarization suppressed DRM and promoted RWGS. Under stoichiometric conditions, both reactions were enhanced, with selectivity determined by the polarity of the applied potential. Transient experiments at 380 °C confirmed reversibility of EPOC and its ability to dynamically steer selectivity. Reactive oxygen uptake provided insight into electrochemically active surface area and promotion mechanisms. These findings demonstrate the potential of EPOC to modulate the H₂/CO ratio and tailor selectivity in reforming processes, with relevance to renewable energy and biogas utilization.